1. Field of the Invention
The present invention relates to a contact member for controlling an electrostatic state of a member to be charged or discharged, and in particular, to a charging brush for charging a surface of an electrostatic latent image carrier such as a photosensitive drum in an image forming apparatus such as a copying machine and a printer, and specifically, also relates to a discharging brush for removing a residual charge on the electrostatic latent image carrier with contacting the carrier to discharge the residual charge.
2. Description of the Background Art
The contact member such as the charging brush and the discharging brush is usually formed of a group of brush hairs contacting the surface of the electrostatic latent image carrier. The contact member charges the surface of the carrier at an intended potential by applying a charging voltage to the brush hairs, or removes a residual charge on the carrier.
Particularly, the contact member such as the charging brush and the discharging brush, which includes cellulosic fibers such as rayon fibers as a major component, has attracted the attention, because of its good creep property, facility in adjustment of an electric resistance and others.
However, if the brush hair (e.g., electrically conductive rayon brush hair) comprising the cellulosic fiber(s) and conductive material such as carbon black dispersed therein is used, the fiber may contact a conductive substrate or base member of an image carrier, which is maintained at a ground potential and is exposed through a pin hole in the surface of the image carrier, in which case an excessively large current flows through the fiber, so that the hair catches fire, and the fire spreads to other hairs. The spread of fire is due to the fact that the cellulosic fiber has high flammability and burnability.
Accordingly, it is an object of the invention to provide a contact member for controlling an electrostatic state of a member to be charged or discharged without the above mentioned problems.
It is another object of the invention to provide a contact member such as a charging brush and a discharging brush in an image forming apparatus, which can prevent inflammation and spread of fire of brush hairs, which may be caused by an abnormal current flowing though a pin-hole or the like in an electrostatic latent image carrier.
It is still another object of the invention to provide an improvement of a contact member including cellulosic high polymer fiber as a major material which is liable to generate heat and inflame due to the flow of current, and more particularly, an improvement of a contact member in the form of a brush having a small volume and a small heat capacity, conversely to a brush of a roller type.